MANCHESTER — Carol Shea-Porter, the Rochester social worker who became the darling of New Hampshire’s liberal activist corps 12 years ago, stunned the political elite again with shocking news that in 2018 she won’t seek a fifth term representing the First Congressional District.

Shea-Porter, a grandmother recently for the first time, turns 65 this December.

She said in a brief, heartfelt statement Friday that family ties were behind this unexpected decision.

“I felt the tug of family at our reunion on Independence Day, and I have continued to feel it,” Shea-Porter said in a statement a few hours after she told her surprised staff. “My family has said repeatedly that they would support any decision I made, and I am grateful to them for that and for all of their love and support through the years.”

Shea-Porter’s move throws wide open what already was shaping up as one of the dozen most competitive, U.S. House seats in the country in next year’s midterm elections.

“It’s a total surprise, nobody saw this coming,” said Kathy Sullivan of Manchester, who was Democratic Party chairman when Shea-Porter’s first upset win in 2006 capped off a historic sweep for Democrats up and down the ballot.

“She always surprised people. She surprised people when she won and she surprises people on her way out. Carol always marched to her own drummer and it worked.”

Back in that race, Shea-Porter was the activist who went to then-Congressman Frank Guinta’s town halls as a critic and helped form a group that wore T-shirts to President George W. Bush rallies that said, “Turn Your Back on Bush” in symbolic protest of the Iraq War.

The Democratic Party establishment handpicked as its 2006 candidate State Rep. Jim Craig, at the time minority leader in the New Hampshire House of Representatives.

Shea-Porter went on to crush Craig and then unseat two-term Republican Congressman Jeb Bradley in this district that makes up the eastern half of New Hampshire from Conway to Seabrook.

“I first won in 2006 without a single paid staffer because of their hard work,” Shea-Porter said. “I also thank Republican and independent voters for their confidence, and I have listened to their concerns as well. Coming from a Republican family, I know that we need to hear each other, even if we don’t always agree on policy.”

Democrats expected to take a serious look at running are Executive Councilor Chris Pappas of Manchester, former Portsmouth City Councilor Stefany Shaheen, State Sen. Donna Soucy, D-Manchester and former AFL-CIO President and Manchester State Rep. Mark MacKenzie.

State Sen. Andy Sanborn, R-Bedford, and former, state liquor agency law enforcement chief Eddie Edwards of Dover are already mounting GOP campaigns and many think ex-Vice Chairman Matt Mayberry of Dover is edging towards his own bid.

Earlier this week, former two-time candidate John Stephen of Manchester cited his family and business demands in ruling out a 2018 run.

Other Republicans who could give this race a renewed look include former hopefuls Dan Innis, a New Castle state senator, Portsmouth businessman Sean Mahoney and Bradley.

“First I would like to thank Congresswoman Carol Shea-Porter for her years of public service,” Sanborn said in a statement.

“While we had differences of opinion about the future of our county there is no doubt that in her years of service she always did what she thought was best for the people of New Hampshire.”

“I made the decision to run for Congress because I wanted to see serious change in Washington and I know that I am still the best candidate to fulfill that vision.”

Edwards also wished Shea-Porter well.

“It has become apparent to me as I travel across this district that the voters are hungry for something other than just another politician,” Edwards said. “They yearn for honesty and integrity, and they are begging for results.”

Shea-Porter had four showdowns with former Congressman Frank Guinta, losing the seat in 2010 and 2014, winning it back in 2012 and 2016.

Guinta has already said he won’t run again, Shea-Porter stressed she’ll stay politically involved after next year.

“I have great faith in our ability to overcome challenges and to come together again, and I will continue to speak out,” Shea-Porter concluded.

“As Granny D, New Hampshire’s champion for campaign finance reform, said, ‘Democracy is not something we have, it’s something we do.’ And as I always add, it will go away if we don’t “do” democracy by engaging on the issues and voting. I am greatly encouraged by the heightened civic engagement I am seeing.”